EP2297840A1

EP2297840A1 - Arc welding set with an optimized quasi-resonant soft-switching inverter

Info

Publication number: EP2297840A1
Application number: EP09794028A
Authority: EP
Inventors: Peyofougou Coulibaly
Original assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude; Air Liquide Welding France
Current assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude; Lincoln Electric Co France SA
Priority date: 2008-07-07
Filing date: 2009-07-01
Publication date: 2011-03-23
Also published as: WO2010004190A1; FR2933546A1

Abstract

Quasi-resonant soft-switching inverter comprising: means (4, 6) for connection to an electrical power supply (8) having a DC voltage supply terminal (6) and a reference terminal (4); a first switching cell (30₁) and a second switching cell (30₂), of quasi-resonant type, which are connected in parallel between the supply terminal (6) and the reference terminal (4), characterized in that it further includes: a passive switching pole associated with a first switching cell (30₁); an active switching pole associated with the second switching cell (30₂); a device for controlling said switching cells (30), which delivers signals to a dual thyristor module with logic control; and a device (28) for controlling said active switching pole, said device being synchronized with said device for controlling the switching cells (30).

Description

Optimized quasi-resonant soft-switching inverter arc welding station

The present invention relates to an improved soft-switching quasi-resonant type power source and an arc welding station comprising this inverter, as well as a method for controlling the power delivered by this inverter or substation. welding.

There are inverters for delivering continuous output voltages that operate according to a principle known as "soft switching quasi-resonant". The electrical diagram of such an inverter is known from the document

EP-A-1564876. Switching from a state to a blocked state is done in a conventional manner and the rise gradient of the voltage across the switches is advantageously slowed by the capacitors placed in parallel. Switching from a blocked state to an on state can be performed at zero voltage according to the principle of soft switching to zero voltage, upon receipt of a boot command issued by the controller. Indeed, the reactive energy stored in the resonance elements makes it possible to obtain at the output terminals of the cells conditions enabling switching from the off state to the on state corresponding to a soft switching of the so-called "at zero" type. voltage "or ZVS (Zero Voltage Switching).

Such circuits have a number of advantages, including the reduction of switching losses and electromagnetic disturbances. However, the smooth switching operation of these circuits occurs only for a certain operating range because it depends on the level of the output current and the supply voltage.

This is problematic, particularly in the field of arc welding, since it requires currents whose intensity must vary over a wide range, from vacuum to short circuit. Management of the dead time according to the current is often carried out between the switches of the same switching cell, but this solution proves very complex and in fact inefficient. Moreover, the setting of the power, at fixed frequency, is achieved by a so-called "phase shift" command between the cells. This introduces an operating asymmetry, so that the late-phase cell loses smooth switching operation below a certain large limiting current.

An increase in the value of the inductance in series with the transformer makes it possible to extend the range of operation in soft commutation, but this method leads to a loss of power duty cycle ratio and to oscillations across the diodes of the transformer. secondary rectification assembly.

A number of techniques already exist to improve the performance of this basic structure. Very common techniques are to place auxiliary circuits at the secondary of the inverter transformer, to switch a switching cell in zero voltage mode (ZVS) and the other cell in zero current mode or ZCS (Zero Current Switching), a principle known in the literature by the acronym ZVZCS (Zero Voltage Zero Current Switching). The performances of these circuits are often mediocre. EP-A-1564876 and US-A-6016258 are also known, in which the soft switching is obtained over the whole range of variation of the load by using the energy stored in the inductive components of two auxiliary circuits, called " switching poles ", placed on the primary side of the transformer on each arm of the bridge. This eliminates the loss of duty cycle and significantly reduces spurious oscillations across the secondary diodes. On the other hand, these auxiliary circuits increase the losses by conduction in the main switches and can seriously deteriorate the efficiency of the inverter. The insertion of a control circuit in these auxiliary circuits can reduce losses by conduction, but its management proves difficult, if not impossible. In addition, management of the dead time between the switches of the same switching cell is essential to avoid sudden discharges of capacitors in the switches or to avoid the return to operation in conventional hard switching. The operating reliability of the inverter is not completely guaranteed by this dead time management, which limits the operating frequency of the inverter for high powers. In addition, these auxiliary circuits do not support the abrupt control changes necessary for welding.

To solve the problems of adjusting the dead time between the switches, a "dual thyristor" type control card can be used. The principle of such control circuits is described in document FR-A-2 564 662 and more specifically in EP-A-1564874 in the context of quasi-resonance. Unfortunately, this board operates only over a certain range of welding current, since the zero voltage spontaneous ignition conditions are no longer fulfilled below a certain current value.

A problem to solve is therefore to propose:

- an inverter does not have the aforementioned drawbacks and reliably allows smooth switching over the entire operating range in welding, vacuum short circuit, high power and high frequencies, with reduced overall losses; an arc welding station comprising such an inverter; and a method of controlling the power delivered by such an inverter or such a welding station.

The invention relates to a quasi-resonant inverter with a soft switching circuit, comprising: means for connection to an electric power supply source comprising a DC voltage supply terminal and a reference terminal,

a first quasi-resonant switching cell and a second switching cell connected in parallel between the DC voltage supply terminal and the reference terminal,

characterized in that it further comprises:

a passive switching pole associated with the first switching cell; an active switching pole associated with the second switching cell;

a device for controlling said switching cells, delivering signals according to a dual thyristor logic, and

a device for controlling said active switching pole, synchronized with said control device for the switching cells.

The poles referred to above are auxiliary circuits intended to facilitate switching of the switching cells. A pole is normally associated with a switching cell. Their role is to provide an additional current to the main switches of these cells allowing a smooth switching, ie a lossless operation in the switches during the initiation or blocking phases.

In the so-called "passive" pole, the elements are non-controlled and can be in particular capacitors, inductors, resistors, transformers, etc. The current flowing through them is not controlled and the pole delivers current continuously in the main switches of the switching cells.

In the so-called "active" pole, the current delivered by the pole is controlled. It can comprise passive elements of the same type as those of the passive pole, but especially of the controlled elements such as switches. It may include other ordered elements. The active pole supplies current only at the time of the switching phase of the main switches of the switching cell concerned. This reduces the additional losses in the switches, at the cost of increasing the complexity of the switching pole.

In the inverter according to the invention, the first switching cell needs a relatively low current to switch; a passive pole is therefore sufficient and the losses remain limited. On the other hand, the second cell may require a large current to switch if there is an asymmetry in the control of the characteristic switching cells. out of phase. The active pole then makes it possible to avoid excessive energy losses.

According to particular aspects of the present invention, it may have one or more of the following features:

- The inverter has two switching cells.

Each switching cell comprises two switches connected in series between the power supply and reference terminals, as well as an output terminal taken between these two switches, each switch being connected in parallel with a capacitive element. "Switch" or "capacitive element" must, here as in the remainder of this description, be understood in terms of function; that is to say that each switch or capacitive element may consist of several elements together ensuring a switch or capacitor function. To constitute a switch capable of passing a certain power, the skilled person may in particular put several switches in parallel. It can do the same for capacitive elements.

- The passive switching pole comprises:

. a capacitive divider formed of two capacitive elements arranged in series between the supply and reference terminals,

. an intermediate supply terminal taken between these two capacitive elements, connected to the output terminal of said first switching cell via an inductive element and whose potential varies between the potentials of said supply terminals and reference, and

. two diodes connected in series between the supply and reference terminals, and in parallel with each capacitive element. Here, as in the remainder of the description, the inductive elements may naturally consist of several elements that together perform this function and the diodes may consist of several elements that together perform this function.

- The active switching pole comprises:

. a capacitive divider formed of two capacitive elements arranged in series between said supply and reference terminals,

. an intermediate power terminal connected between these two capacitive elements and connected to the output terminal of said second switching cell by means of an inductive element in series with a head-to-tail connection of two switches controlled by said control device of the active pole, and. two diodes connected in series between the supply and reference terminals, and in parallel with each capacitive element.

- The control device of the switching cells comprises: . a control device delivering control signals corresponding to blocking commands or boot permissions,

. a circuit for detecting the voltage between the power electrodes of each switch delivering logic two-state voltage signals comprising a high state corresponding to a voltage between the electrodes of substantially zero power and a low state corresponding to a voltage substantially different from zero, and

. a control circuit receiving said control and voltage signals and delivering to each switch of the switching cells a control signal corresponding to a blocking command when said control signal corresponds to a blocking command and / or when the voltage between the power electrodes is substantially different from zero, or corresponding to a priming authorization when said control signal corresponds to a priming authorization and the voltage between the power electrodes is substantially zero.

The switches of the switching cells are of MOSFET type and controlled in dual thyristor mode and the switches of the active switching pole are of the IGBT type and controlled in thyristor mode.

The control device of said switching cells supplies to said first switching cell corresponding to the passive switching pole control signals in advance of a given duration with respect to the signals delivered to said second switching cell corresponding to the active pole; .

- The control devices of the active switching pole and the switching cells deliver synchronized control signals as follows:

. the ignition command transmitted by the control signal of a first switch of the active switching pole is in advance of a given duration, or advance time, on the blocking command transmitted by the control signal of the switch of the switching cell in which said first switch is capable of delivering a current,

. the duration of the control signal of said first switch of the active switching pole is greater than or equal to twice said advance time,

. the ignition command transmitted by the control signal of the second switch of the active switching pole is also in advance by a duration equal to the said advance time on the blocking command transmitted by the control signal of the switch of the switching cell in which said second switch is capable of delivering a current, and

. the duration of the control signal of said second switch of the active switching pole is greater than or equal to twice said advance time.

According to another aspect, the invention also relates to an arc welding station, characterized in that it comprises at least one inverter according to the invention. This arc welding station may further comprise the following elements:

a DC voltage source connected to at least one inverter whose output terminals form the welding terminals,

an associated control device, means for inputting a welding setpoint connected to said control device of said at least one inverter.

According to another aspect, the invention relates to a method of controlling the inverter or the welding station according to the invention, delivering a given power, characterized in that the power delivered is increased or decreased, respectively, by reducing or reducing increasing, respectively, the advance of the control signals of the first switching cell corresponding to the passive switching pole with respect to the control signals of the second switching cell corresponding to the active switching pole.

The invention will be better understood on reading the following description and examples, which are not limiting. They refer to the attached drawings, in which:

FIG. 1 represents an electrical diagram of an inverter according to the invention,

- Figs. 2A to 2K represent the various sequences of the operation of the inverter described with reference to FIG.

- Figs. 3A to 3F represents a timing diagram of various signals during operation of the inverter described with reference to FIG. 1,

FIG. 4 is a block diagram of an inverter welding machine according to the invention.

According to an exemplary embodiment described in FIG. 1, the inverter 38 is connected between the reference terminals 4 and 6 supply, the DC voltage source 8, which delivers a DC voltage of about 600 volts.

The inverter 38 comprises two cells or switching arm 30i and 3O ₂ , arranged in parallel between the terminals 4 and 6 and each having two switches connected in series between the terminals 4 and 6. These switches are designated generally by reference numeral 32 and in a particular manner by the references 32 _{ljl 5} _LJ2 32, 32 _2JL and 32 _2, 2. The switches 32 are arranged in parallel with a capacitive element 34 for switching assistance and forming a resonance element. In the example, the switches 32 are so-called MOSFET type switches such as for example the components designated IXKN45N80C. The capacitive elements 34 are capacities of 4.7 nF (nano-farads). The switching cell 30i has an output terminal 36i between the two switches 32 ₁ and 32 ₁ and the switching cell 30 ₂ has an output terminal 36 ₂ between the switches 32 ₂ , i and 32 ₂ , ₂ .

The inverter 38 also comprises a transformer 40 consisting of two coupled 4O1 and 4O ₂ transformers, whose windings are connected in series to the primary and parallel to the secondary. The primary is connected in series to the outputs 36i and 36 ₂ of the two switching cells 30. The secondary is connected to a diode rectifier 47 and 48 delivering a DC voltage of the inverter output. The transformer 40 is in the example a planar transformer coupled with twice 10 kW, this technology being particularly suitable for high power and high frequency applications. Such a transformer is conventional in the field of power electronics and will not be described in more detail.

The inverter 38 also comprises an inductive element 42 arranged in series between the output terminal 36i of the first switching cell 30i and the primary of the transformer 40. This inductive element 42 is an optional element intended to reduce the electromagnetic disturbances. thanks to its influence on the rate of rise and fall of the current at the primary level. Optionally, this inductive element 42 is formed by the leakage inductance of the transformer 40. In the example, this inductive element 42 consists of the leakage inductance of the transformer 40 with a value of 1.2 μH (micro-Henry) .

The secondary of the transformer 40 is connected to a rectifier 44 of conventional type using DSEP 2x101 diodes (400 volts of twice 100 A), and a current smoothing inductance 49 of a value of 10 μH. The output terminals of the rectifier 44 directly form the output terminals of the inverter 38 and are designated by the reference 46. The inverter 38 comprises a first passive switching pole consisting of a capacitive divider 311 formed of two elements. capacitors 55i, i and 55 _li2 arranged in series between said power supply terminals 6 and reference 4, said capacitive divider 31 ₁ comprising a terminal taken between the two capacitive elements and forming an intermediate power supply terminal 561, the output terminal 36i said cell 30i being connected to the intermediate power supply terminal 56i via an inductive element 58i, and diodes 53i, i and 53i, ₂ connected in series between the power supply terminals 6 and reference terminals 4, and in parallel with each capacitive element 55i, i and 55i, ₂ , In the example, the capacitive elements 55 i, i and 55i, ₂ are capacitors of 10 nF; the element 58i is an inductance of 80 H and the diodes 53 _U and 53 _U are of the BYT30P-1000 type (30 A, 1000 V). The inverter 38 comprises a second switching pole, active, consisting of a capacitive divider 3I ₂ formed of two capacitive elements 55 ₂ , i and 55 ₂ , ₂ arranged in series between said power supply terminals 6 and 4, said capacitive divider 3I ₂ having a terminal taken between the two capacitive elements and forming an intermediate terminal 56 ₂ , the output terminal 36 ₂ of the cell 30 ₂ being connected to the intermediate power supply terminal 56 ₂ via an inductive element 58 ₂ , arranged in series with a head-to-tail arrangement of two switches 70 and 71 controlled by a device 28, and diodes 53 _2il and 53 ₂ , ₂ connected in series between the supply terminals 6 and reference 4, and in parallel with each capacitive element 55 _2il and 55 ₂ , ₂ .

With the addition of the switches 70 and 71, the current in the pole is delivered only during the switching phases, which reduces conductive losses in the switches 32 _2jl and 32 ₂ , ₂ . In the example, the capacitive elements 55 _2il and 55 ₂ , ₂ are capacitors of 1 F; the element 58 ₂ is an inductance of 3 H, the diodes 53 _2il and 53 ₂ , ₂ are of the BYT30P-1000 type; the switches 70 and 71 are IGBTs (600 V, 100 A) connected in anti-series.

The inverter 38 also comprises a control device 18 delivering control signals to the switches 32 corresponding to blocking commands or priming authorizations. Such a command is performed by a so-called "dual thyristor logic" principle and will be described in more detail later with reference to FIG.

The inverter 38 furthermore comprises a control device 28 delivering control signals StIi ₁ and StIi ₂ to the switches 70 and 71 corresponding to synchronous initiation or blocking commands of the control signals Sc _2il and Sc ₂ , ₂ of the controller 18. These signals are adapted to provide pulse type currents for switching the switches 32 _2j1 and 32 ₂ , ₂ in zero voltage mode (ZVS). The operating principle of this command is described later.

The circuit as described makes it possible to obtain at the levels of the output terminals 46, using a 100 kHz operation command of the type controlled blocking and spontaneous ignition, a voltage of 0 to 50 volts and a current of 0 at 500 amps. In fact, the switching poles make it possible to obtain the spontaneous ignition of the switches 32 without any lower current limit.

Moreover, the components used, in particular in the inverter, can be made in several different ways.

The switches 32 may be conventionally formed from one or more identical MOSFET transistors placed in parallel, so that the switches as a whole are unidirectional in voltage and bidirectional in current. The capacitive elements 34 and 55 may be formed of several capacitors arranged in parallel. The number and nature of each electronic component used varies according to the maximum power that the inverter must deliver.

The operation of a circuit according to the invention will now be described by way of example with reference to FIG. 1. The circuit being of a periodic periodic operation In this example, it will be described in half a period with reference to the sequences shown in FIGS. 2A to 2K and the timing diagrams of the different signals in FIGS. 3A to 3E. On these timing diagrams, the voltage and the intensity across different components are represented, referenced respectively by the letters V and I with the component number in index. The commands of each of the main and auxiliary switches 70, 71 are also shown in the timing diagram of FIG. 3A, a blocking state appearing as a low level signal and a boot state in the form of a high level signal, as well as their time offsets.

The operation of the circuit is decomposed according to eleven sequences SO to SlO.

Initial sequence SO (Fis.2A): active phase of power transfer

The switches 33i, i, 33 ₂ , 2 and the diode 47 conduct while the switches 33i, 2, 33 ₂ , i and the diode 48 are blocked. The primary windings of the transformer 40 see a positive constant voltage (V40 = Vs). The current in the output filter inductor 49 is returned to the primary via the diode 47 and the transformer 40. The current of the switch 33i, i is the sum of the current in the output inductance 49 brought back to the primary and the current in inductance 58i of the switching pole. This sequence ends, blocking the switch 33i, i by the command.

Sequence Sl (Fis.2B): Controlled blocking of the switch 33ij and linear phase of charging and discharging the capacitors 34i, i and 34i, 2

At the beginning of this sequence, the switch 331, 1 is controlled by the blocking and no other change of state of the switches occurs during this interval, the duration of which is the charging and discharging time of the capacitors 34 ₁ and 34 ₁ ₂ . Since the switch 33i, i is off, the sum of the current in the inductance 42 and in the inductance 58i of the passive pole begins to charge the capacitor 34 ^ ₁ and discharge the capacitor 34 _1j2 simultaneously. The voltages at the terminals of the 2 switches 33i, i and 33 _li2 are translated, respectively by the equations:

Vαα,, = Vα, = Ve - m V ,, = V, = m

2 C 34,

34, 2 C 34,, t: current time

C34 'C34 _{1 2} : capacity of capacitors 34y and 34 ₁ 2m: transformation ratio of transformer 40. Due to the presence of capacitor 34 _{ljl 5} the voltage across the switch 33i, i can only grow slowly, allowing reduced losses to blocking.

The capacitor 34 _li2 discharges during this time interval. Once it is fully discharged, the diode 35 _LJ2 antiparallel with the switch 33 _LJ2 closes spontaneously, allowing the continuity of the current. The voltage across the switch 33i, 2 is kept at zero creating the conditions of spontaneous ignition in zero voltage mode (ZVS).

Sequence S2 (Fis.2C): Freewheel phase without power transfer

Since the diode 35 _li2 is _conducting , as the switch 33 ₂ , ₂ is still on, the primary winding of the transformer 40 sees a zero voltage after the cancellation of the voltage across the capacitor _li2 . The voltage across the diode 48 is zero and the two diodes 47 and 48 are then passing in a freewheel mode. The primary current in the transformer 40 is kept constant. The current in inductance 58i begins to grow from the negative peak value. The duration of this freewheel phase is determined by the phase shift time t _α required to adjust the power transfer.

Sequence S3 (2D Functions): Controlled Priming of the Switch 71

The auxiliary switch 71 is started. The current in the inductor 58 ₂ starts to grow from zero. The switch 33 ₂ , 2 sees the sum of the primary current in the transformer 40 and the current in the inductance 58 ₂ .

Sequence S4 (Fis.2E): Blocking diode 53i, i

The diode 53i, i of the passive pole is blocked and the continuity of the current is ensured by the capacitors 55i, i and 55 _li2 of the passive pole. The instant of blocking of this diode 53i, i depends on the parameters of the passive pole (value of the inductance 58i and the capacitors 53i, i and

Sequence S5 (Fis.2F): Controlled blocking of the switch 332.2 and oscillatory phase of charge and discharge of the capacitors 342, i and 342.2

At the beginning of this sequence, the switch 33 ₂ , ₂ is controlled blocking. The current in inductor 58 ₂ is at its peak peak value. No other switches change state during this interval. The duration of this interval is the charging and discharging time of the capacitors 34 _2jl and 34 ₂ , ₂ . Similar to sequence 1, this current starts charging the capacitor 34 ₂ , ₂ and discharging the capacitor 34 _2jl . The voltage across the capacitor 34 ₂ , ₂ begins to grow from zero, while the voltage across the capacitor 34 ₂ , i begins to decrease from the supply voltage 8. As soon as the voltage across the terminals of the capacitor 34 ₂ , i capacitor 34 _2jl begins to decrease, the transformer 40 begins to see a negative voltage because the diode 34i, ₂ is already passing. The current of the output inductance 49 is brought back to the primary via the diodes 47 and 48 and the transformer 40.

Since this interval is very short, the current in inductor 58 ₂ remains almost constant at its peak peak value.

As in sequence 1, we find:

Due to the effect of the capacitor 34 ₂ , ₂ , the voltage across the switch 32 ₂ , ₂ can only grow slowly ensuring limited loss blocking switching for the switch 32 ₂ , ₂ . The gradual discharge of the capacitor 34 _2jl zero the voltage across the switch 32 _2jl during this interval, allowing the spontaneous ignition in zero voltage mode of the switch 32 _2jl .

During this interval, the current of the arm 30 ₂ is equal to the sum of the current in the output filtering inductance 49 brought back to the primary and the current in the inductance 58 ₂ . However, the ripple of the current in the inductor 49 is at its low value (this shows the opposite effect of the ripple of the current of the load on this arm during the commutation), and taking into account the resistances of the components _li2 and ₂ , ₂ , the primary current is damped and is not perfectly constant during the freewheel phase. This reduces the current constraints of the switch 33 ₂ , ₂ to the blocking but also reduces the current required to discharge the capacitor 34 _2jl . To obtain the spontaneous ignition of the switch 32 ₂ , i, the capacitor 34 ₂ , i must be totally discharged during the time allotted to it (dead time for example). Otherwise, if it is not completely discharged due to insufficient amplitude of the current, the switch 32 ₂ , i will lose spontaneous initiation switching. With conventional control, the energy stored in the capacitor 34 ₂ , i will be suddenly discharged into the switch 32 ₂ , i at its initiation. In the case of a dual thyristor logic, the inverter stops naturally.

Sequence S6 (Fis.2G): Linear phase of decay of the primary current

At the beginning of this sequence, the diode ₂ i spontaneously initiates in zero voltage mode. No other change of state of the switches occurs during this interval. As the diode 35 _2He is conducting, the inductor 58 ₂ sees a constant negative voltage -V _8/2. The current begins to decrease linearly according to the equation:

V ₈ I ⁵⁸ ₂ ^{= ~} ^ i ^{t + I} 58 ₂ max

58 ₂

L ₅₈ : value of inductance 58 ₂

Sequence S7 (Fis.2H): Linear phase of decay of the primary current and spontaneous blocking of the switch 71

The auxiliary switch 71 is blocked spontaneously. From this moment, its StIi ₂ signal can be extinguished. The primary current continues to decrease linearly. This sequence ends the blocking of the diodes _I ₂ and I ₂ as the currents passing through these diodes cancel each other out.

This sequence depends on the parameters of the active auxiliary circuit and time t _r control phase advance of the auxiliary switch 71.

Sequence S8 (Fis.21): Linear phase of decay and inversion of the primary current

The diodes 35 1 ₂ and 35 ₂ block spontaneously when the primary current is canceled. The continuity of the current is provided by the main switches 33 _li2 and 33 ₂ , i, if they are already controlled at boot.

Sequence S9 (Fis.2J): Blocking the secondary diode 47

The secondary diode 47 spontaneously locks when the primary current in the transformer 40 has reached the current imposed by the load.

Sequence SlO (Fis.2K): spontaneous priming of diode 531.2

The diode 53 _li2 of the passive pole spontaneously initiates the cancellation of the voltage across the capacitor 55 _li2 .

This sequence depends on the parameters of the passive pole.

Switches 33 _li2 and 33 _2il are on and switches 33i, i and 33 ₂ , ₂ are blocked. The diode 53 _li2 is on and the diode 53i, i is blocked. This sequence is symmetrical to the initial sequence So. Another operation cycle symmetrical to the previous 11 sequences begins and the converter then periodically repeats the operation process.

The operation of the active pole of the example will now be described by showing the synchronization of the commands 28 of the auxiliary switches 70 and 71 with the commands 18 of the main switches 32.

The auxiliary switch 70 (respectively 71) is initiated with a phase advance t _r before the blocking of the switch 33 _2il (respectively 332,2). This phase advance and the value of the choke 582 determines the duration and the peak value of the current pulse sent to the main switch to switch to zero voltage.

The operation of the circuit and waveforms in the various elements are shown in Figure 3E to the switching of the switch 332,2- It is assumed that the capacitors 55 and 552.2 _2He are important values (e.g. the order of 1 F) to have constant voltages at their terminals during switching.

Initially the primary current in the transformer 40 is assumed to be positive and flows in the main switch 332.2. To start the switching process,

V ₈ auxiliary switch 71 is controlled at boot. A voltage of - ^ - is applied across the inductance 582 and the current in it increases linearly with a slope

V ₈ of -. During this time the main switch 332,2 remains on.

^{2 L} 58 ₂

When the current in inductance 582 reaches its maximum peak value determined by the time t _r and the value of inductance 582, the switch 332.2 is controlled at blocking. A resonance phase begins and the capacitor 342,2 is charged, while 34 ₂ , i discharges. When the voltage across the capacitor 34 _2JL passes through zero, the diode 35 _2He begins spontaneously. The main switch 32 _2jl can now be _ignited under zero voltage. Once the diode ₃₅₁ leads, the current in the inductor 582 decreases to zero with a slope of -. From this moment, the auxiliary switch 71

^{2 L} 58 ₂ hangs at zero current. Peak current in inductance 582 is given by:

! _{582 ITmX} = - - - 0 _* : phase advance time of thyristor control

^{2 L} 58 ₂

71 with respect to the lock command of the switch 332,2) The total switching time is given by: t _c = 2 t _r At a high load current, the energy stored in the inductor 42 may be sufficient to switch the main switches 32 _2j1 and 32 ₂ , 2 to zero voltage. In this case, the commands of the auxiliary switches 70 and 71 can be inhibited.

We will now show the functional features of the passive pole clipped the example, of the elements 58i, 55 _{lil s} _li2 55, 53i, i and 53 _li2.

The shape of the current is oscillatory with a flat portion whose duration depends on the values of the elements 58i, 55i, i and 55 _Ij2 and the switching frequency fc of the inverter. The voltages at the terminals of the capacitors 55i, i and 55 _li2 are discontinuous and vary between 0 and the supply voltage Vs.

The natural frequency of the resonant circuit is given by:

Cu _r fP = 27 ^ 2 C ₅₅₁ ₅₈₁ L 2π With _55i C = C = C _55i _55n ₂ (value capacitors liabilities pole). The values of the capacitors 55i, i and 55 _li2 are identical. Let α _{f be} the ratio between the operating frequency of the inverter and the natural frequency of the passive pole, ie

¹ C

The peak amplitude is given by the expression:

I _5S1 m _a x = 2C _55i V ₈ (2π f _p ) = 2 V ₈ C _55i ω ' ^J .P For the same peak of current 1 _{58i inax} , the duration of the flat portion due to clipping is a function of α _f with:

^V ^8/1 max ^V SS ₁ ^8/1 SS ₁ max max h ^ / ^V ^ 8 h max / ^V 8

L 'o, = = and 2 L', = =

¹ 2π α _f f _c ω _p ^ι 2 π α _f f _c ω _p

The minimum current of the pole for smooth switching to zero voltage is given by: 1 _{SS1 I} m _n = V ₈ ^ 2C _34l / L ₄₂ , with C ₃₄₁ = C ₃₄ ^ ₁ = C ₃₄ ^

Calculations and simulations make it possible to determine the value of the components for the pole circuit as a function of the switching aid capacitors 34 ₁ and 34 ₁ ₂ .

For control with sudden and large phase shift variations, a sufficiently flat bearing portion is required to maintain the same peak current level.

We will now describe the dual thyristor logic control principle of the example. The purpose of this piloting is to solve the problem of management of the dead time between switches of the same cell by naturally making the commutations complementary.

This control is characterized in that it comprises a circuit for detecting the voltage between the power electrodes of each switch of the inverter delivering voltage signals and a control circuit receiving said control signals transmitted by the control circuit. as well as said voltage signals and adapted to deliver to each of the switches a control signal corresponding to a blocking command when said control signal corresponds to a blocking command and / or when the voltage between the power electrodes is substantially different from zero and corresponding to a priming authorization when said control signal corresponds to a priming authorization and the voltage between the power electrodes is substantially zero.

According to the embodiment described in FIG. 1, the power source comprises a control device 18 outside the inverter 38 and adapted for a forced control of blocking the switches 32 and their spontaneous ignition. Each of the switches 32 receiving a signal Sci, i, Sci, 2, Sc2, i and Sc2,2 carrying blocking commands or priming authorizations.

The control signals Sc of the switches 32 of one and the same cell are complementary to one another and the control signals of two opposite switches of a diagonal are out of phase for the adjustment of the power transfer. Thus, the signals Sci, i and Sci, 2 are complementary, as are the signals

Sc2, i and Sc2,2, and the signals Sc1, i and Sc2,2 are out of phase, as are the signals Sci, 2 and Sc2, i. In particular, the signals Sci, i and Sci, 2 are out of phase with respect to the signals Sc ₂ , i and Sc ₂ , 2.

Each of the circuits 50 comprises an inverter comparator 52, connected between the terminals of the switches 32, so as to compare the voltage levels of each of the terminals, or to compare the voltage across the switches 32 with respect to zero.

For each detection circuit 50, a reference voltage generator 54 is furthermore interposed between an input terminal of the comparator 52 and a terminal of a switch 32.

This reference voltage is low relative to the maximum voltage that can appear between the power electrodes of a switch 32, for example of the order of 17V.

Thus, each circuit 50 allows the detection of a zero or almost zero voltage, across a switch 32. The detection of such a voltage results in the emission of a voltage signal St which is in a state logic high when the voltage across the corresponding switch 32 is zero or almost zero and in a low logic state the rest of the time. Finally, the device also comprises an additional control stage formed of a control circuit 60 interposed between the control device 18 and the switches 32. This circuit 60 receives as input the control signals Sc emitted by the control device 18 and that the voltage signals St emitted by the detection circuits 50. In the embodiment described, the control circuit 60 comprises several logical units 62 designed to perform, for each switch 32, a logic function AND between its control signal Sc and its voltage signal St and deliver a control signal Sp to the corresponding switch 32.

Thus, the logical unit 62 _{1 s2} delivers a signal Sp _li2 which corresponds to a logic function AND between the control signal Sc _li2 intended for the switch 32 _lj2 and the voltage detection signal St ₁₁₂ delivered by the circuit 50 _li2 detecting the voltage across the switch 32 _lj2 .

In the embodiment described, the driving signal Sp is directly applicable to each of the switches 32. Depending on the nature of the switches 32, an adaptation circuit can be inserted between the output of the logic units 62 and the switches 32 in order to to allow the generation of a control signal adapted to the switches.

In operation, the control signals Sc delivered by the controller 18, have two levels corresponding to a high logic state for a boot enable and a low logic state for a lock command.

The control circuit 60 therefore transmits a blocking command by supplying each switch 32 with a low level logic control signal Sp when it has received a control signal SC of the same logic level and / or when the difference in potential across the switch 32 is greater than the reference voltage generated by the generator 54, that is to say when the signal St is at a low level.

The blocking commands issued by the control device 38 are therefore directly transmitted to the switches.

On the contrary, a priming authorization corresponding to a control signal Sc with high logic high level, will be transmitted only when the detection of a zero or almost zero voltage across the corresponding switch, it is i.e., when the voltage detection signal St is also at a high level.

The device therefore makes it possible to ensure that the switches 32 of the inverter 18 receive a priming authorization issued by the control device 18 only when the voltage at their terminals is zero or almost zero. The application of such a control circuit to the inverter 38, thus prevents a short circuit on a switching cell of the inverter, thus increasing its reliability. In addition, the overall efficiency of the inverter is improved by eliminating or at least reducing the required dead time between the boot controls and the existing blocking commands in the state of the art inverters. , the control of such an inverter is thus simplified.

With reference to FIG. 4, an example of an inverter arc welding station according to the invention will now be described.

The welding station 100 is connected to an electrical energy transfer network, for example a three-phase network 102. This three-phase network 102 delivers alternating voltages to a rectifier 104 forming a DC voltage source to which an inverter 108 is connected. corresponding to the inverter 38 as described with reference to Figure 1. The rectifier 104 and the inverter 108 thus combined form a power converter between an AC voltage source and a DC voltage source and vice versa.

The output terminals of the inverter 108 are connected to terminals 110 forming the welding terminals for carrying out an arc welding.

Furthermore, the welding station 100 also comprises means 112 for entering a setpoint for welding. This instruction is transmitted to a control device 114 corresponding to the control devices 18 and 28 described with reference to FIG. 1. Finally, the control device 114 delivers control signals to the inverter 108 for the formation of a control signal. output to the terminals 110, corresponding to the set point.

Of course, different types of instructions can be envisaged depending on the desired applications. In particular, the inverter of the invention can be used in a smooth or pulsed arc welding station. Finally, although the invention has been described in the context of welding, it is also possible to use the inverter of the invention in other fields of application, for example the charging of rechargeable batteries or stabilized power supplies. common.

The inverter of the invention has a significant number of advantages over existing inverter substations, including:

the reduction of switching losses in the switches, making it possible to access the high switching frequencies, which themselves allow a reduction in the weight, volume and cost of the elements (transformer, inductors, dissipators, etc.),

- the reduction of electromagnetic disturbances,

- smooth switching operation over the whole range of variation of the welding current (from vacuum to short circuit), - The reduction of the losses by switching in the auxiliary switches in the poles by controlling the pulse width of the control signals Sthi and StIi ₂ .

the reduction of the additional conduction losses due to the switching poles,

- the use of semiconductor switches under favorable switching conditions: MOSFET in ZVS mode and IGBT in ZCS mode,

- high operational reliability thanks to the dual thyristor logic: no dead time management and, in the event of erroneous control or non-operation in soft switching, natural shutdown of the inverter.

During tests of the inverter according to the invention, the converter was controlled at a frequency of 100 kHz (200 kHz of output ripple) or 200 kHz (400 kHz output) with a power output of the order of 20 kW. At this power, such control frequencies go beyond what is allowed by conventional inverters. Comparisons with existing inverters have also shown a weight gain of nearly 40% (from 21 kg to 13 kg), for an operating frequency of 100 kHz instead of 40 kHz and the same power of the order 20 kW.

Claims

1. Quasi-resonant, soft-switching type inverter comprising: - means (4, 6) for connection to a power source (8) for electrical energy comprising a DC voltage supply terminal (6) and a reference terminal (4),

a first quasi-resonant switching cell (3O ₁ ) and a second switching cell (3O ₂ ) connected in parallel between the supply terminal (4) and the reference terminal (6),

characterized in that it further comprises:

a passive switching pole associated with the first switching cell (3O ₁ ); an active switching pole associated with the second switching cell;

(3O ₂ ),

a device for controlling said switching cells (30), delivering signals according to a dual thyristor logic, and

a control device (28) of said active switching pole, synchronized with said control device of the switching cells (30).

Inverter according to Claim 1, characterized in that each switching cell (30) has two switches (32) connected in series between the supply and reference terminals (4, 6) and an output terminal. (36) between these two switches, each switch (32) being connected in parallel with a capacitive element (34).

3. Inverter according to one of claims 1 to 2, characterized in that the passive switching pole comprises: - a capacitive divider (311) formed of two capacitive elements (55i, i, 55i, ₂ ) arranged in series between the power supply (6) and reference (4) terminals,

an intermediate supply terminal (56i) taken between these two capacitive elements, connected to the output terminal (36i) of said first switching cell (3O ₁ ) via an inductive element (58i) and the potential varies between the potentials of said supply (6) and reference (4) terminals, and

- two diodes (53 _{lil s} 53 _li2 ) connected in series between the supply terminals (6) and reference (4), and in parallel with each capacitive element (551,1, 55 _li2 ).

Inverter according to one of Claims 1 to 3, characterized in that the active switching pole comprises:

- a capacitive divider (3I ₂ ) formed of two capacitive elements (55 _2il , 55 ₂ , ₂ ) arranged in series between said supply terminals (6) and reference (4), - an intermediate supply terminal (56 ₂ ) taken between these two capacitive elements and connected to the output terminal (36 ₂ ) of said second switching cell (3O ₂ ) via an inductive element (58 ₂ ) in series with a head-to-tail arrangement of two switches (70, 71) controlled by said control device (28) of the active pole, and

two diodes (53 ₂ , i, 53 ₂ , ₂ ) connected in series between the supply (6) and reference (4) terminals, and in parallel with each capacitive element (55 ₂ , i, 55 ₂ , ₂ ).

Inverter according to one of claims 1 to 4, characterized in that the control device of the switching cells (30) comprises:

a control device (18) delivering control signals (Sc) corresponding to blocking commands or priming authorizations,

a circuit (50) for detecting the voltage between the power electrodes of each switch (32) delivering voltage signals (St) with two logic states comprising a high state corresponding to a voltage between the electrodes of substantially zero power and a low state corresponding to a voltage substantially different from zero, and

a control circuit (60) receiving said control (Sc) and voltage (St) signals and delivering to each of the switches (32) of the switching cells (30) a control signal (Sp) corresponding to a control command blocking when said control signal (Sc) corresponds to a blocking command and / or when the voltage between the power electrodes is substantially different from zero, or corresponding to a boot authorization when said control signal (Sc) corresponds to a priming authorization and that the voltage between the power electrodes is substantially zero.

6. Inverter according to one of claims 1 to 5, characterized in that the switches (32) of the switching cells (30) are of MOSFET type and controlled in dual thyristor mode and that the switches (70, 71) active switching pole are IGBT type and controlled in thyristor mode.

7. Inverter as defined by one of claims 1 to 6, characterized in that the device (18) for controlling said switching cells (30) delivers to said first switching cell (3O ₁ ) corresponding to the switching pole of the control signals (Sci, i, Sc _li2 ) in advance of a given duration (t) with respect to (Sc2,2, Sc _2il ) _signals delivered to said second switching cell (3O ₂ ) corresponding to the active pole.

Inverter as defined by one of claims 1 to 7, characterized in that the control devices (28, 18) of the active switching pole and the switching cells (30) supply control signals (Sth, Sc) synchronized as follows:

the ignition command transmitted by the signal (Sthi) for controlling a first switch (70) of the active switching pole is in advance of a given duration, or advance time (t _r ), on the blocking request transmitted by the signal (Sc _2He) of controlling the switch (32 _2, i) the switching cell (3O ₂₎ wherein said first switch (70) is able to supply a current,

the duration of the control signal (Sthi) of said first switch (70) of the active switching pole is greater than or equal to twice said feed time (t _r ), - the boot order transmitted by the signal ( StIi ₂ ) for controlling the second switch (71) of the active switching pole is also in advance by a time equal to said lead time (t _r ) on the blocking command transmitted by the signal (Sc ₂ , ₂ ) for controlling the switch (32 ₂ , ₂ ) of the switching cell (3O ₂ ) in which said second switch (71) is capable of delivering a current, and - the duration of the signal (StIi ₂ ) for controlling said second switch (71) of the active switching pole is greater than or equal to twice said feed time (t _r ).

9. Arc welding station characterized in that it comprises at least one inverter as defined in any one of claims 1 to 8.

10. An arc welding station according to claim 9, characterized in that it further comprises:

- a DC voltage source (104) connected to at least one inverter (108) whose output terminals (110) form the welding terminals, - an associated control device (114),

means (112) for inputting a welding setpoint connected to said device (114) for controlling said at least one inverter (108).

11. The method of controlling the inverter according to one of claims 1 to 8 or the welding station according to one of claims 9 or 10, delivering a given power, characterized in that the power delivered is increased or decreased, respectively, by reducing or increasing, respectively, in advance (t) control signals (Sci, i, S above, ₂₎ of the first switching cell (3O ₁₎ corresponding to the switching pole passive with respect to the control signals (Sc ₂ , ₂ , Sc _2il ) of the second switching cell (3O ₂ ) corresponding to the active switching pole.